The present invention relates to an ultrasonic motor driving circuit which employs a piezo-electric element to generate a driving force for the ultrasonic motor.
The conventional type ultrasonic motor has been driven continuously by supplying a large current of several tens of milliamperes continuously from a battery.
In this type motor, therefore, the battery capacity cannot be utilized effectively.
In general, when a large current is to be derived from a battery, the quantity of current that can be used is less than the capacity of the battery. This may be explained by referring to FIG. 2, which shows load characteristics of a battery. In the figure, curves A, B, C represent load characteristics for three different load resistances (small, medium and large), respectively. When, for example, the final voltage is taken as 2.0 V, the current utilization of each load resistor is some 5418 mAh for the curve A, some 5486 mAh for the curve B and about 5645 mAh for the curve C. This shows that the smaller the current taken out, the more effectively the battery capacity can be utilized.
The conventional drive method that continuously uses a large amount of current, therefore, has the drawback of not being able to make full use of the battery capacity.